I had 7 manual saves in Mass Effect 2. The system there worked perfectly for me. But I am a fan of having manual saves just in case I miss something, or screw up. Or you get to something like the Duke/Duchess of Mania/Dementia quests in Oblivion and end up having to replay the entire Shivering Isles arc because you forget to manual save D:< (in other words, manual saves are good to explore different alternatives)